According to this calculator i found:
Results: First Day of Last Menstrual Period:April 23, 2008
Probable Date of Ovulation: May 7, 2008
Possible Dates of Conception: May 3 to May 11, 2008
Due Date: January 28, 2009 (40 weeks)
Hope this helps a little. Good luck!
Pregnancy is dated by adding two weeks to the date of possible conception (which typically equates to dating from date of last monthly period in most cases assuming a women ovulates on day 14 of her cycle).
If you conceived on May 6th, you would have been 7 weeks, 2 days pregnant on June 12th. i.e. you would NOT be 5 weeks pregnant because you need to add 2 weeks onto the date of possible conception.
That being said, ultrasounds can be up to 1 week off. In any case, it could be either mans child and the only way to find out who the father is is with a DNA test.
going by your lmp your 9 2/7weeks pregnant and conception would have occured around Wednesday, May 7, 2008 so to me it sounds like its your exs.